The present invention relates generally to a magnetic disk cartridge for storing image data, audio data, text data and the like. More specifically, the invention relates to an erroneous erasure-preventing device in a magnetic disk cartridge, which prevents a writing of additional data on the disk in order to protect data previously recorded on the disk.
Various kinds of magnetic disk cartridges are used to record image data, audio data, text data and other signals. One type of magnetic tape cartridge is disclosed in U.S. Pat. No. 4,466,032, issued on Aug. 14, 1984, to Saito, which is assigned to the same assignee as the present invention. This prior art disk cartridge encloses a flexible magnetic disk within a thin box-shaped cartridge. The cartridge defines an opening through which a magnetic head of a disk drive of a recording and reproducing apparatus has access to the disk surface for recording video, audio, text, digital data, and other signals and reproducing the recorded data.
As will be appreciated, when the recorded data are important and must not be inadvertently or erroneously erased, no additional data should be written or recorded onto the disk. One typical method of erasure-prevention in the known art involves a recess or opening at an appropriate point on the cartridge. The recess or opening in the cartridge receives a "write-preventing" lever or pin which prevents a write-head in the recording apparatus from contacting the disk while the lever or pin is within the recess or opening. In early disk cartridges, the recess or opening was sealed by a strip forming part of the cartridge, which strip was broken and removed after important data were recorded. Once the recess or opening covering strip was removed from the cartridge, the strip could not be re-installed on the cartridge to enable that cartridge to receive additional recorded data. Therefore, conventional magnetic disk cartridges have their recesses or openings sealed by adhesive tape or other appropriate means.
In order to make such disk cartridges more convenient to use, a novel magnetic disk cartridge was proposed in U.S. Pat. No. 4,460,930, issued on July 17, 1984 to Takahashi, and assigned to the assignee of the present invention. In the proposed arrangement, the magnetic disk cartridge is provided with an "erasure-preventing" movable piece which can slide between a closing position at which the aforementioned recess or opening is covered and an opening position at which the recess or opening is uncovered to allow entry of a "write-preventing" lever or pin as set forth above. This movable piece in the proposed arrangement is not removed from the cartridge, and therefore allows a repeated change of state of the magnetic disk cartridge between a "write-enabled" state and a "write-inhibited"0 state. In this cartridge, further writing on the disk is enabled when the movable piece is in its recess-closing position. On the other hand, further writing is inhibited when the movable piece is in its recess-opening position.
Although the aforementioned cartridge advantageously allows a repeated change of writing-receiving state of the magnetic cartridge without requiring other means for covering the recess or opening after once being actuated to the write-inhibited state, the presence of the movable piece causes the structure of the cartridge to become complicated and tends to lower the yield and the production rate of the magnetic disk cartridge during manufacture. Especially, in the structure of the aforementioned U.S. Pat. No. 4,460,903, the erasure-preventing piece must be firmly maintained between the upper and lower halves of the cartridge during assembly. This secure position requires a special and rather expensive tool to hold the erasure-preventing piece in place within the cartridge during assembly.
In addition, since the "erasure-preventing" movable piece must be held securely in either the erasure-preventing position or the erasure-enabling position, a detecting mechanism or the like is required. An example of a detecting mechanism is referred to in the 930 'patent noted above. Since a detecting mechanism makes the movable piece rather bulky, the erasure-preventing piece cannot be conveniently used in a relatively small magnetic disk cartridge.
Thus, it remained a problem in the cassette recording and reproducing art to provide a relatively small disk cartridge structure which effectively incorporated a movable erasure-preventing mechanism.